Power unit



April 18, 1961 H. E. PERKINS, JR., ETAL 2,979,895

POWER UNIT Filed Feb. 4, 1958 5 Sheets-Sheet l FIG.

NVENTORS. I HAROLD E. PERK|Ns,JR.

- 'BY DONALD w.HAsK|Ns April 18, 1961 H. E. PERKINS, JR., ET AL 2,979,896

POWER UNIT 5 Sheets-Sheet 2 Filed Feb. 4, 1958 INVENTORS: HAROLD E. PERKINS,JR. BY DONALD W. HASKINS April 18, 1961 l H. E. PERKINS, JR., ET AL 2,979,896

POWER UNIT Filed Feb. 4, 1958 5 Sheets-Sheet 3 FIG. 3 f3 34 7 34 50 50 34 INVENTORSZ HAROLD E. PERKINS,JR. DONALD W. HASKINS United States atent:`A`

APOWER UNIT c This invention relates to a power unit of the solid propellant type and more particularly to a propellent gas generating explosive cartridge of the type designed for starting a load such as an engine or the like by producing a large volume of gas for a relatively short time.

Gas turbines, for example, such as the propulsion units of jet aircraft are engines which are not self-starting; and explosive cartridges have ben employed to supply gas at high velocity and pressure` for impingement against the blades of a rotor4 element to start u'p such turbines. Such4 cartridges contain an exothermically decomposable 'substance such as powder which burns without detonation, and` generates a large volume of gas rather slowly but at a relatively rapidly rising temperature and pressure.V The powder may advantageously be a massive pellet or giant grain of particles of nitrates, chlorates or perchlorates set in an oxidizable matrix, or it may consist of a single base or double base smokeless powder or various combinations of these and any other suitable substances. This cartridge main charge may have its lateral or end surfaces suitably inhibited to obtain any desired'type of slow surface burning with the particular powder of the composition otherwise tailored for the task upon ignition. Burning must occcur steadily at great and mounting pressure but without equipment damaging violence or excessive fragmentation of the grain. On discharge of the cartridge the generated gas fed through suitable channels is directed by nozzles upon the rotor blades of either an auxiliary or main turbine which accelerates the rotor assembly of the main engine until it becomes self-driving.

The cartridge isI generally cylinder housed or held as' an expendable item in asuitable breech mechanism whichrprovides a cartridge reaction chamber as a permanent structure rechargeable by insertion therein of another exo'thermically decomposable charge; One wall of atypical chamber has an ignition connection such as an,

ignition electrode for Vadmitting iiringelectric current to the vcartridge while another portion of the chamber wall has a discharge portfor the generated gases; and the chamber has-in one of the best arrangements a breech opening and closing means provided circumferentially in thecylindrical side wall. InV any event, it is vdesired that the cartridges be such as to. permit easy extraction of a spent cartridge, that burningproduce nov fouling, that sealing of the reaction chamber at the breech be effective to prevent'leakage of the generated gas and that .the charge of exposive or. other burnable gas evolving substance be firmly mounted in the chamber in reliable ignif tionrelationship with the igniter.vr The cartridge should perform well at extremes of temperature and pressure.

. y' Therefoi'e,,one vof l the` objects lof thisv invention vis the provision Iof-Ha well ysealelpo/wer cartridge capable -of evolving a gasfathighpressure, withfaminimum loss of pressurefromleakage.; f if f I -Another object vis reliabilitylof ignition.

.ztAnothert-obiectfis toprovide al gas generating power i surface of the side walls` ofthe reaction chamber, In

Patented Apr. 18,1961

unit or cartridge which'is so sealed that it burns its charge without excessive fouling of the reaction chamber.

Another object s to provide such a gas generator cartf ridge which upon expenditure ofits burning charge may be readily extracted for replacement of a fresh cartridge. Another object is to provide a cartridge which seats itself firmly in the breech mechanism to assure properelectrical contact and to avoid any looseness which might permit the burning grain to be shoved and broken.

Still another advantage is the provision of gasV generator cartridge capable of performing satisfactorily over a wide temperature range including extremes of hot and cold and over a wide range of pressures particularly the extremes likely with jet aircraft.

A further object is the provision of a cartridge struc-'- ture which may'not only be readily and economically manufactured but which also is suiciently sturdy to take rough'handling without coming apart or developingI failures of performance. Y

These and otherobjects and advantages will be better understood from a description of one specic embodiment of the invention when taken in conjunction with the accompanying drawing in which:

Figure l is a longitudinal cross sectional view showing one preferred specific embodiment of the cartridge loaded into a typical breech or reaction chamber with the clear- -ances at the bottom exaggerated to between show the structure involved;

Figure 2 is a transverse cross sectional view of the embodiment of Figure l taken on line II-II; and

Figure 3 is an enlarged fragmentary view showing one form of the portion of the cartridge at the igniter end wall in cross section before the cartridge is loaded into the reaction chamber.

In accordance with this invention there is provided a power cartridge ofvsuch construction and composition as to have not only improved sturdiness over a broad range of ambient temperature but also resilience both longitudinally and transversely and adequate resistance to heat built into the cartridge case so as to assure improved reliability of ignition and sealing. This is achieved in great part by provision of a suitable elastomeric outer shell of proper wall thickness and of suitable protuberant configuration of one of the'end walls.

A case. of heat insulating rubber of the type resistant to* the cartridge as a completed unit including the rubber case and all other of its parts must be able to take mechanical beating equivalent to a four foot drop from any position to a concrete slab without becoming disassembled and/ or inoperative. It will be understood that other suitable heat resistant elastomers such as silicone rub--` bers are contemplated. Thev rubber case hasa thickness of from about 0.045 to about 0.125 of an inch but preferably of about 0.100 of an inch so as to have appreciable resistance to burning through while at the same time remaining capable of being stretched both longitudinally and circumferentially when fired so as to obtain-V expansion of the case at least in the side walls to put-it into snug form-fitting relationship with the inner the side walls the rubber case is undersized in length and diameter to leave sufficient clearance to avoid interference which might prevent or make difficult loading the largest cartridge into the smallest breech within manu facturing tolerances.

Adjacent one end the elastomeric case forms the discharge end adapted to carry a closure consisting of pres sure limiting sealing diaphragm together with a gas outlet grating having a sufficiently large number of perforations therein of desired size for the necessary discharge of the working gases rdeveloped by the reaction in the chamber. This end of the cartridge faces the exhaust l port of the reaction chamber. f

Thek opposite end of the elasticV case is closed by a bottom wall integral with the relatively short cylindrical side walls and characterized according to this invention by a more protruding dome shapeV than a` corresponding relatively oblate recession in the bottomof the end wall of the mating part of the reaction chamber.` An insulated electrode is positioned in the end Wall of the reaction chamber and adapted to .engage an electrical contact pin carried in the back of the dome; An insulated spring ground Contact is also carried by the dome. These contacts serve to actuate the device by means of an igniter charge disposed within the case in a readily disintegratable receptacle mounted in the case between said igniter dome-shaped end wall and the opposed end face of the powder charge. The elastic dome-shaped end wall also includes a number of radiallydisposed longitudinal ribs extending integrally from said end wall adjacent the roof portion thereof but falling short of the axial central or peak portion of said end wall as Well as being spaced from the cylindrical side walls so as to provide a well in the center for reception of the igniter and so as to leave no radial connection between dome and side acting in opposition to distension of each. These longitudinal ribs provide a stiffer but still resilient support and spacer for the propellent charge with respect to the igniter dome. This assures proper positioning of the cartridge in the reaction chamber and provides shock absorption for the propellant charge to avoid cracking of the grain in the event of accidental blows to the cartridge such as might occur should it be inadvertently dropped or caused to collide with some of the permanent breech structure during loading to start an engine. This special construction of the ribs also provides a resilient stiffening support for the dome surrounding the more pliant peak or center of the dome at the electric contacts thereof without adversely affecting the pliability of the center. By being sloped at the end faces adjacent the propellant grain the support for the grain is only at an outer peak of each rib leaving the adjacent ignitable face of the grain exposed at least at the central portion which is closest to the igniter and most effectively ignited. Thus, the ribs also act as spacers for the end face of the charge.

The elastomeric case must in any event remain sufficiently resilient for satisfactory obturation over a broad ambient temperature range of from about 75 F. to about 250 F. at least, or even to about 500 F. or higher maximum for silicones, or the like.

Another feature of this invention lies in the resiliently loaded evanescent igniter assembly afxed to the resilient domed end of the elastomeric case. The assembly comprises a relatively wide flat end faced igniter contact pin for contacting the breech electrode in electric connection with one side of the electric ignition circuit and ground contact spring electrically insulated from said pin for contacting the grounded breech structure connected to the other side of the circuit. The igniter is encased in a receptacle of polyethylene or the like. The polyethylene merely melts and vaporizes in the flame and does not throw the pressure off by deagration.

t In one form of this assembly the pin is affixed with respect to the assembly and the domed end in either slightly projecting relationship from the end of the case as shown in Figure 1, nearly flush relationship, or in slightly recessed relationship largely as determined by the degree of projection of the electrode pin of the case. In this form the resilience of the case assures reliable electric connection between cartridge and breech mechanism and compensates for most variations in the cartridge and chamber lengths and often for the pin length too. To give maximum compensation for all variations, however, the contact pin of the cartridge is spring loaded outwardly and floats to always meet the mating electrode in the breech. The plunger type also affords ush dis tension of the case about the pin so as to minimize chances of a break or cut at this point in the rubber case.

The igniter receptacle consists of a box with a lid detachably but dependably aflixed both at the rim and at the center to the box so that the igniter ash composition is not spilled during handling before firing. The box also contains an electric squib.

At the screened discharge end of the cartridge there is provided a pliant member in the form of a pellicle or membrane capable of resisting the heat at least momentarily and of holding not only any pressure differential that may develop as a result of ambient changes as those due to altitude changes, for example, but also holding at least the minimal pressure for sustained gas evolution when the membrane is bulged against the steel grating during firing. The membrane remains unruptured at the perforations having a diameter of about fyi@ of an inch until the minimal pressure is achieved. The pellicle is a plastic lm which preferably is free from plasticizer and is evanescent in the presence of the fiame and develops higher strength as the temperature falls so as to automatically compensate for the higher minimal pressure needed at lower flame temperatures of operation which varies around 2,000 F.

A polyethylene film having a thickness of about 0.004 0.010 of an inch depending upon the grade and molecular weight and preferably of about 0.006 was found especially suitable for consistent sustained ignition. Milar lm about 0.001 of an inch thick was also found suitable. In any event, the strength of the pellicle must be such as to resist rupture and delay escape of the gas until the minimal pressure has been reached and until the rubber case seals itself in the breech chamber.

The propellent charge is either a pressed, extruded or cast massive pellet of cylindrical shape either surface coated in whole or part or uncoated as needed, and can be either solid or tubular. Its cylindrical surfaces can be provided with inhibitors and heat insulators where double end burning is desired. Solid spacers may be provided between the outer cylindrical surface of the grain and the inner surface of the case. Also the discharge opening of the reaction chamber may be at the same end as the igniter. To assemble the pellet and rubber case, the pellet is first pushed into the open end of the case, as it is forced open and held stretched, and then one end of the pellet is seated upon the tips of the rubber case ribs at the closed domed end. It remains clamped between these tips acting on one end and an internal shoulder at the case opening acting upon the other end of the pellet.

In the drawing, Figure 1, a tubular pellet 2 is coated at surfaces 21 and 22 leaving the ends 24 and 25 opposite ribs 12, 13, 14 and 15 adjacent the tips uninhibited.

Figure 1 shows a breech structure 100 in which is positioned a cartridge 200 illustrating a specific embodiment of this invention.

The cartridge confining breech mechanism consists of a stationary metal receiver 101 having a closed end except for an exhaust portion 112 thereat and an internal shoulder 113 near Ythis end against which cartridge 200 is seated upon its beingloaded into the receiver. Thevother vone solid piece.

arrasar E .2 with the grooves 104 of the'corresponding open end of receiver 101.V l Portions 101V and 102 when put together forma reaction chamber having cylindrical side walls intermediate the ends of which there' is a circumferential parting line 105 at which opening and closing of the breech occurs. The opposite end of closure member 102 is formed with a dished closed end 110 at the center of which there is an igniter nipple 108.` Mounted in lid 102 between the electrode and the nipple 108 integral with the dished end is a sleeve of electrically insulating material 107 carrying electrode 106. One side of the electrical ignition system for the cartridge is connected to the metal receiver 102 through the dished end 110 and the spring ground contact 31 carried by the cartridge case 200. The other side of the ignition system is connected to the electrode 106.A

The gas generator cartridge shown in this embodiment consists of a particular rubber case structure 1 containing a tubular shaped charge 2 of ignitable gas evolving material, an igniter assembly 3, a rupturable weather sealing closure membrane 4 and a perforated rigid metal grate 5.

Charge 2 is a giant grain of thermally decomposable material having, for example, an outer coating 21 and an interior coating 22 on the cylindrical faces of the grain so as to leave the end faces uncoated and adapted for ignition and burning.

This charge 2 is mounted between the annular shoulder 10 of the elastomeric cartridge case 1 and the radially extending ribs 12, 13, 1'4 and 15 extending longitudinally from the domed end wall 16 integral with the cylindrical side wall v11 of the case 1. The ribsA12, 13, 14, and 15 are rooted tothe ldome wall 16 but separated from the cylindrical side wall 11 so as not to impair the resiliency of the side wall 11 and end dome wall 16. Opposite the side wall 11 the ribs are spaced from the central axis and in part at the base are joined to an annular flange 17 which with the ribs defines an igniter case well 17 adjacent the peak 18 of dome wall 16 for receiving the igniter assembly 3. The ends of ribs 12, 13, 14, and facing the giant tubular grain 2 are slanted away from the'grain endjthe nearer the axis so` as to leave a wedge-shaped space 19 between each rib and the adjacent end face of grain 2 largest near the igniter for more complete access and resultant uniform ignition of this end face upon actuation of the igniter assembly 3. Opposite the domed end wall 16 the elastic case is provided with a circumferential groove 20 for seating the peripheral edge of a moisture proof pressure resistant, but relatively thin, membrane 4 and for seating the circumferential edge of the relatively rigid grate or screenmember 5. Although any dome shape such as a parabolic one more protruding at the peak than the receding cavity in the end of reaction chamber 100 is contemplated, the double bulge or more bulged peak 18 shown in Figure 1 is preferred as the short radius of curvature gives maximum resilience at the peak at the igniter contacts where most needed.

Igniter assembly 3 in the preferred embodiment shown in Figure 3 consists of a polyethylene box or cup 35 closed with lid 34. The lid is provided with snap brim 34" about its periphery and a thick boss 50 about its small central opening 34. Snap brim 34" engages the open end of cup 35 and boss 50' is positioned about the collar button rivet end of spring retainer end 50. The box contains a charge 39 and an electric squib 40 connected by lead wires to terminal clips 37 and 38 which are mounted to contact the hollow contact post 51 and contact eyelet rivet 33 respectively. Post 51 forms a spring housing tube for pin spring 53 pushing on contact pin plunger 52 to form a contact unit consisting of parts 50, 5152 and 53, which in another embodiment may be This unit is electrically insulated by sleeve 36 from the other unit consisting of eyelet 33 and ground contact 31. One flange 33' of eyelet 33 together with the other ange 33" holds the loaded cup, electric contact units including spring contact bai 31 all together 6` about ya perforation in the end ofthe bulge 18 at the peak of the dome 16. l v

In operation when the cartridge 200 is shut in breech mechanism 100 the clearances and resilience of the case 1 are such as to thrust the entire cartridge toward the igniter electrode 106 leaving some clearance between the cartridge case domed end 16 and the dished end 110 with the least if any, clearance adjacent the electrode and the surrounding area, as shown diagrammatically at line 16' and exaggerated at 16. This avoids any jamming of the largest cartridge with the smallest breech `and still assures good ignition contact between pin 32 and electrode 106 and between ground 31 and wall 110, with thesmallest, i.e., shortest cartridge in the largest breech. When pin 32 becomes a plunger 52 of the floating type as in Figure 3, or is fixed ilush or even recessed with the resilient end of the dome, the dome 'peak can at least during maximum pressure be put ilush'with dished end 110 about its elec-A trode 106 which is the best condition. This is true whether the dome 16 has a generating radius smaller than that of dished end 110, or the shape is more parabolic or has the central more resilient bulge 18, the latter of which ispreferred.

VWhen the tiring circuit is closed squib 40 sets off igniter charge 39 to completely disintegrate lid 34 and cup 35 and commence ignition of faces 2.4 and 25 of grain 2 with concomitant bulging of membrane 4, side walls 11 and dome 16 to more nearly at least the position shown diagrammatically by line 16" and normally even into full engagement with dished end 110. This means that as the pressure rises to the point of self-sustaining pressure and burning the case 1 is sealing itself in the breech so as to prevent any gas leakage to parting line of the breech and to prevent gas by-pass tending to foul .the area adjacent electrode 106. Upon rupture' of membrane 4, burning of the propellent charge and the resultant gas generation continues at a steady pace and at the desired energy level. After the charge 2 has been consumed the breech lid 102 may be lifted off part 101 at 4any time for easy removal of the remaining parts of the case 200 in onepece due to resilience and other factors and if desired replacement of an unspent cartridge.

It will be vunderstood that although the foregoing isV now believed to be the best embodiment of this invention, those skilled in the art may make modifications and other changes without departing from the spirit and scope of the-inventionv as set forth in the appended claims.

What is claimed is:

l. For a gas generating reaction in a rigid cylindrical breech mechanism having a discharge port and at least one fixed contact electrode passing through an end wall thereof and having a joint at which said mechanism may be opened and closed circumferentially intermediate the ends of the cylindrical wall; an electrically ignitable gas generating assembly comprising a cylindrical cartridge case closed at one end by a dome-shaped wall integral with the case, said case being formed of heat resistant elastomeric material pliant over a temperature range from about 75 F. to about 500 F. with a hardness corresponding to a Shore Durometer number from about A45 to about A70, and containing a slow burning propellent composition, said case carrying ignition means and being provided at the dome-shaped end with an external contact passing through said end for connection with said breech mechanism electrode, said case being receivable in said breech mechanism with clearance space, the other end of the case being spanned and closed by a refractory foraminous port means for discharging at high pressure the gases evolved on reaction of said ignited composition and by port closure means rupturable at a predetermined minimal pressure at and above which the burning of the propellent composition is selfsustaining and the cylindrical wall of said case is distended to span said clearance space thereby placing the case firmly into sealing contact with respect to said joint 7 and electrode during said gas evolution, and the contact bearing end of said case normally protrudingthe most at said contact and a suicient distance to place said contact in connection resiliently with said xed electrode.

2. The assembly of claim l wherein the contact at the end of the case is resiliently mounted to protrude, from said end into positive contact'with the xed electrode.

3. For a gas generating reaction in a rigid cylindrical breech mechanism having a discharge port and at least one xed contact electrode passing through an. end wall thereof and having a joint tat which said mechanism may be opened and closed circumferentially intermediate the ends` of the cylindrical wall; an electrically ignitable gas` generating assembly comprising a cylindrical electrically insulating cartridge case f heat resistant elastomeric material pliant over a temperature range from about 75 F. to about 500 FA with a hardness corresponding to a Shore Durometer number from about A45 to about A70, and containing a slow burning propellent composition, said case carrying ignition means and beingprovided at one end with a resiliently yieldable dome having an external contact passingthrough said dome for connection with said breech mechanism electrode, said case being receivable in said breech mechanism with clearance space, the other end of the case being spanned and closed by a refractory foraminous port means for discharging at high pressure the gases evolved on combustion of said propellent composition and by port closure means rupturable at a predetermined minimal pressure at and above which the burning of the propellent composition is selfsustaining and the cylindrical wall of said case is distended to span said clearance space thereby placing the case firmly into sealing contact with respect to said joint and electrode during gas evolution, said portion of the dome carrying said contact normally protruding the greatest distance from the cy-lindrical wall and sufficiently to place said contact in connection resiliently with said fixed electrode.

4. The `assembly of claim 3 wherein the contact consists of an outwardly urged spring loaded pin.

5. The assembly 0f claim 4 wherein the contact at the resilient end of the case is resiliently mounted to protrude from said end into positive contact with the fixed electrode.

6. A power gas generating cartridge for an engine starterand the like comprising a charge of a propfellel'lt` composition coniined'within a cylindrical casing closed at one end by'a dome shaped end 'wall integral `with the casing', an electrical igniter element within Vsaid casing adjacent the dome shaped end wall andv an ignitable surface of said propellent charge, said casing being formed of a heat resistant elastomeric material having ashore Durometer hardness number from about A to about A within the temperature range of approximately 70 F. and about 500 F. Aand having a thickness between about 0.045 inch and about 0.125 inch, said casing having a discharge opening opposite the dome shaped end Wall, said discharge opening being spanned by a heat resistant grating and by a rupturable pressure limiting sealing diaphragm of sufficient thickness to span said opening until the combustion of the propellent charge is self-sustaining and until the elastomeric case is distended.

7. The cartridge of claim 6 wherein the'dome shaped end of the cartridge has internal longitudinally extending ribs spaced from the side walls and from the central axis of the cartridge and wherein theY end faces of the ribs are sloped so as to contact the propelllcnt charge adjacent the side wall of the cartridge and to provide a tapering ignition space which increases in sizeas it approaches the central axis of the cartridge.

References Cited in the le of this patent UNITED STATES PATENTS 2,529,465 Wallace et al. Nov. 7, 1950 2,713,768 Livingston et al July 26, 1955 2,733,568 Dickinson Feb. 7, 1956 2,776,623 Bonner Jan. 8, 1957 2,816,418 Loedding Dec. 17, 1957 2,920,564 Rhodes Jan. l2, 1960 2,937,493 Adelman May 24, 1960 FOREIGN PATENTS 26,430 Great Britain Nov. 29, 1907 642,684 Great Britain Sept. l6, 1950 742,120 Great Britain Dec. 21, 1955 

